Cooling of combustion chamber walls

ABSTRACT

Means for providing a connection between an upstream element and a downstream element, offset towards the outside in relation to the latter, in a flame tube of a combustion chamber which is intended to function in an external flow of pressurized air. The connecting means comprise an annular solid body adapted to connect the said upstream element to the said downstream element and a thin tongue which is located in the extension of the upstream element and defines, with the downstream element, an annular duct into which there emerges a plurality of regularly spaced passages which pass through the said solid body in the general direction of the external flow in such a way as to take, from the latter, a current of air which is adapted to form, downstream of the annular duct, a film of cooling air on the inner surface of the downstream element. Each passage comprises an upstream bore which emerges coaxially, via an abrupt widened portion, into a downstream bore having a greater cross-section and an appreciable length which itself emerges into the annular duct.

United States Patent n91 Caruel et al.

[111 3,811,276 [451 May 21,1974

[ COOLING F COMBUSTION CHAMBER WALLS Zrimary Examiner-Jisrton R. Croyle ssistant Examiner o ert E. Garrett [75] Inventors Jacques Emlle Jules Canjel Attorney, Agent, or Firm-Watson, Cole, Grindle &

Dammarle-les-Lys; Herve Alain Watson 1 Quillvr, lssy-les-Moulineaux; Jean-Pierre Jules Emile Castellant, Chartrettes; Armand Jean-Baptiste [57] ABSTRACT Lacroix, lu vill ll f France Means for providing a connectlon between an upstream element and a downstream element, offset [73] Assgnee' W Natlonale D Etude f towards the outside in relation to the latter, in a flame co'lstruchon de Moteurs d Avlatlon tube of a combustion chamber which is intended to Pans France function in an external flow of pressurized air. The [22] Fil d; O t, 6, 1972 cgnnecing means cgmprisie an annular solid bogy a apte to connect t 6 Sat upstream e ement to t e ['21] Appl' 295585 said downstream element and a thin tongue which is located in the extension of the upstream element and For i A li ti p i ig p t defines, with the downstream element, an annular 0':t 8 197 France 71 36330 duct into WhlCh there emerges a plurality of regularly spaced passages which pass through the said solid [52] U 5 Cl /39 60/39 66 body in the general direction of the external flow in [5 ll hit Cl n r F02c h such away as to take, from the latter, a current of air [58] Fieid 65 39 66 which is adapted to form, downstream of the annular duct, a film of cooling air on the inner surface of the [56] References Chad downstream element. Each passage comprises an upstream bore which emerges coaxially, via an abrupt UNITED STATES PATENTS widened portion, into a downstream bore having a I Barnwell et al. 0| greater cross section and an appreciable length 3.369363 2/l968 Campbell 60/ 39.65 itself emerges into the annular.duct 3,038,309 6/1962 Waters... 60/39.66 I 3.589.128 6/1971 Sweet 60/39.65 6 Claims, 10 Drawing Figures I j k X I BACKGROUND OF THE INVENTION The invention relates to combustion chambers of the type used, in particular, in turbo-jets for air craft. A

, combustion chamber of this kind is intended to effect the combustion of a fuel in a high-pressure airflow. It is contained in a casing called a flame tube, which is disposed in the flow of air. The flame tube is closed at its upstream end, and combustion occurs in the chamber at a pressure which is lower than that of the external air flow.

In order to create, within the chamber, the turbulence required for the rapid completion of the mixing phenomena which condition the aerothermochemical processes of combustion, a current of air is introduced through the flame tube by orifices of suitable dimensions in the form of jets which form a large angle with the general direction of the flow of hot gases in the chamber. If the orifices are disposed correctly, a short combustion zone is obtained which properly fills the cross-section of the flame tube, which is consequently subjected to a considerable heat flux.

It is'therefore necessary to cool the flame tube, and it is known to introduce into the chamber, for this purpose, air which has been taken from the high pressure flow, in such a way as to form a film of air on the internal surface of the flame tube in order to protect it from the direct action of the flame. This method of cooling is known as film cooling.

In order to introduce and form the film ofcooling air,

- it is possible to employ the expedient illustrated diagrammatically in FIG. 1 of the accompanying drawings, which is a view, in longitudinal section, of part of a flame tube 1 which is immersed in an external flow of pressurized air 2 and separates the latter from the space 3 which forms the combustion chamber. This expedient consists in separating, by means of struts 4, an upstream ferrule la from a downstream ferrule lb which is offset towards the outside in relation to the latter, in

such a way as to maintain, between the ferrules la and lb, a slit 5 through which me external air passes into the chamber 3 at a speed V while licking the inside face of the ferrule lb. At 6, there have been shown the orifices mentioned above, through which an inclined jet of air enters at a speed The slit 5.is highly permeable, so that the current of cooling air is very great and P its speed V, IS likewise very great, being of the same order of magnitude as the speed V J of the jet and .of the order of 2 to 4 times the speed of flow of the hot gases in the combustion chamber 3. Hence the degree of thermal protection afforded by the film of air decreases very rapidly in the downstream direction, starting from the outlet of the slit 5, since-the cooling air mixes with the hot gases. Fundamental tests have shown that th e effectiveness of the film of air is greater if the speed V,'of the cooling air is less than, or equal to, the speed V: of the hot gases.

In order to slow down the cooling air, it has already been proposed that use be made of a low-permeability arrangement which is illustrated in FIGS. 2 and 2a of the accompanying drawings, in which FIG. 2 is a view similar to that in FIG. I, and FIG. 2a is a view in partial transverse section along the line A-A in FIG. 2. In this arrangement, the anterior end of the ferrule lb forms a shoulder 10 joined to an edge 1;! which is welded, at

12, to the ferrule la. The latter is extended by a tongue 7 behind the shoulder lc which is pierced by a plurality of regularly spaced orifices 8, the total cross-section of which is smaller than that of the slit 5 in FIG. 1.

This arrangement has the drawback, which may be a serious one in certain applications, that it requires a relatively long tongue 7. The constriction in cross-section created by the orifices 8 in fact gives rise, in the thin jets of air flowing in the downstream direction, to a heterogeneousness and a turbulence which can only be dampened, in order to produce an effective film of air on the internal face of the ferrule lb, if the tongue 7 is sufficiently long. Since the internal face of this tongue is not cooled and is exposed directly to the flame, the mechanical and thermal behaviour of a long tongue is defective.

FIG. 3 shows another known form of construction, in which the downstream ferrule lb is connected to the upstream ferrule la by a connecting part 9 which is constituted by a solid cannular-like solid body which is mechanically machined in such a way as to form air inlet holes 8a which emerge under a tongue 7a. Compared with that in FIG. 2, thisform of construction offers the advantages that it connects the ferrules of the flame tube in a more solid manner and has better behaviour in respect of heat. However, the holes 8a weaken the part 9; in order to improve its mechanical strength and reduce its permeability, it isnecessary to provide holes 8a which have avsmall diameter and are fairly remote from one another, with the result that the drawback of FIG. 2 is encountered again; a fairly long tongue 7a would be required in order to obtain a regular and homogeneous film of air, but if the tongue is extended, it ,will not be properly cooled and its mechanical and thermal behaviour will be jeopardized.

SUMMARY OF THE INVENTION The object of the present invention is to provide improvements to this connecting part which will make it possible to remedy the above drawbacks.

According to the invention, the air inlet holes are caused to emerge, via abrupt widened portions, into larger holes of appreciable length which themselves emerge under the tongue. Because of their length, the air flows in a regular manner in the downstream portion of these larger holes while occupying the entire crosssection"thereof, with the result that a relatively short tongue is sufficient to produce the film of cooling air from these regular flows which are not far apart from one another. A

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be further described with reference to the accompanying drawings, which are givenv by way of non-limitive examples and in which:

FIGS. 1 to 3 are the explanatory drawings mentioned in the introduction to the present description;

FIG. 4 illustrates a connecting part according to the invention, viewed in section along the line IVIV in FIG. 5; I

FIG. 5 is a view in partial section, along the line VV in FIG. 4;

FIG. 6 is a viewsimilar to that in FIG. 4 and illustrating the flow of the cooling air;

FIG. 7 is a view similar to that in FIG. 6, but showing a variant form;

DESCRIPTION OF PREFERRED EMBODIMENTS In FIGS. 4 to 6 there can be seen a portion of a flame tube 10 which forms one wall of acombustion chamber 11 and is immersed in an external flow of pressurized air 12 supplied by the compressor of an aircraft turbojet which is not shown. This portion of flame tube 10 comprises a cylindrical, upstream ferrule 10a connected, by a connecting part 13, to a cylindrical, downstream ferrule 10b which is offset towards the outside in relation to the upstream ferrule 10a. The connecting part 13 comprises a solid cannular-like body 14, two cylindrical and flanges I and 16 which have, respectively, the same diameters as the ferrules a and 10b and are respectively welded to the latter at 17 and 18, and a cylindrical tongue 19 which is located in the extension of the flange l5 and defines, with the flange 16, an annular duct 20 into which there emerge a plurality of passages 21 which are regularly'spaced out over the circumference of the body 14 and pass through the latter axially, that is to say, in the general direction of the flow 12.

As has been explained in the introduction to the pres ent description, the chamber 11 is the seat of a combustion process which occurs'at a pressurewhich is lower than that of the flow 12. The passages 21 are designed to take, from the external flow. 12, a current of air which is adapted to form downstream'of the annular duct 20, a film of cooling air on the internal surface of the downstream ferrule 10b.

In accordance with the present invention, each passage 21 comprises an upstream bore 22 which emerges coaxially, via an abrupt widened portion 23, into a downstream bore 24 of greater cross-section, which itself emerges into the annular duct 20. It will be seen from FIG. 6 that, because of the relatively great difference in pressure between the external flow l2 and the combustion chamber 11, the cooling air which enters the upstream bores 22 at 25 becomes detached from the walls of the said bores. The length 11 of these upstream bores 22 is sufficient to permit the air to become reattached to their walls, while forming, in each of them, an air flow which occupies their entire crosssection. The air passing out of the .upstream bores 22 undergoes a loss of pressure because of the abrupt widened portions 23 and forms jets 26 in the downstream bores 24, and the latter have a length 12 which is suffcient-to permit the jets 26 to reattach themselves to their walls while forming, in each of them, an air flow which occupies their entire cross-section. The cooling air passing out .of these downstream bores 24 emerges, via a second widened portion 30, into the annular duct '20, while undergoing a new loss of pressure and forming jets which reattach themselves to one another and to thewalls l6'and 19 of this duct over a relatively short length 13. Y

The tongue 19 may therefore be of moderate length. In order to produce a connecting part 13 which functions correctly, the-following rules will preferably be observed in respect ofdimensioning:

the minimum width e', of the solid radial parts be-- tween downstream bores 24 is selected to be as small as is technologically possible; it is expedient to note that these bores 24 may be very close without jeopardizing the mechanical strength of the part 13, since the stresses to which this part is subjected mainly pass into the body 14 through the major solid radial parts of larger minimum width e,

between the upstream bores 22;

the length 1 of the tongue 19 is greater than, or equal to, 6e it may be very close to this value;

the cross-section of the downstream bores 24 is, at the most, equal to four times the cross-section of the upstream bores 22; in the form of construction illustrated, the bores are circular and the ratio of the diameter d; of the downstream bores to the diameter d of the upstream bores, is between 1 and 2.

the length 1 of the downstream bores 24 is a least equal to about three times the difference between their diameter d and the diameter d, of the upstream bores 22; I

the length l, of the upstream bores 22 is equal to at least twelve tenths of their diameter, that is to say,

to 1.2 d,.

The connecting part 13 illustrated makes it possible, in the case of the combustion chambers of modern engines, which are subjected to very high thermal stressing, to guarantee the two qualities which are of prime importance, namely efficient cooling and good mechanical and thermal behaviour of the part. It has low bulk and weight and satisfactory rigidity. It can be manufactured -easily and cheaply. I I

The advantageous effects of the invention are obtained through .the cooperation of the downstream bores with the upstream bores and with the annular duct limited bythe tongue, and also through the two successive, abrupt widened portions 23 and 30. If the passages passing through the body 14 were to have a constant cross-section from the entry to the exit, (known arrangement shown in FIG. 2), it would not be possible to obtain a sufficiently slow-moving and uniform film of cooling air with a sufficiently short tongue. If these passages were to have, for example, the diameter d of the downstream bores, the film of air would pass out at a uniform, but excessively high, speed. If the passages were to have the diameter d,, the flow and speed of the air mightbe suitable, but the spacing-out of the orifices would necessitate a tongue having an undesirable length, in order to obtain a uniform speed of the film of air on its departure-As regards the successive widened portions, these produce, in the flow of air, graduated losses of pressure which, if the speed of departure of the film of air remains the same, give rise to a less pronounced degree of turbulence, which makes itpossible to shorten the length of tongue necessary for rendering the film of air homogeneous.

It is obvious that the forms of construction described are only examples and that they could be modified, particularly by the substitution of technical equivalents, without thereby departing from the scope of the invention. In particular, although the contraction of the flow 'at the entrance to the upstream bore gives rise to a loss of pressure which is useful for slowing down the flow, it would not constitute a departure from the scope of the invention to chamfer the entrance to this bore, for

example in the manner indicated-in FIG, 7, in which those elements which perform the same function as in the preceding figures are designated by the same reference numerals, with the addition of the index a. In this figure, the entrance to each of the upstream bores 22a is chamfered at 27, which offers the advantage of eliminating or minimizing the detachment of the air 25a and therefore makes it possible to slightly shorten the upstream bores 22a.

Nor would any departure from the scope of the invention be constituted by the removal, for example by milling of part of that portion of the body of the connecting part in which the downstream bores are formed, or preferably of an outer part of the said portion, as shown, for example, in FIGS. 8 and 9, in which those elements which perform the same function as in the preceding figures are designated by the same reference numerals, with the addition of the index b. In this form of construction, that portion 28 of the cannularlike body 14b in which the downstream bores 24b are formed, is cutaway in its outer part in such a way as to form an annular duct 29 which extends around the peripheral part of the duct 20b in the upstream direction and into which the outer parts of the upstream bores 22b emerge. The downstream bores 24b thus have the shape of open troughs on the duct 29.

Other embodiments and modifications of the connecting part are possible without departing from the spirit and scope of the invention as defined-by the appended claims.

What is claimed is l. A multi-ferrule flame tube having an upstream ferrule (10a), a downstream ferrule (10b) stepped outwardly with respect to said upstream ferrule, and an integral union member (13) interposed between said ferrules and comprising:

an upstream cannular-like section (14) having an inner end flange (15) fast with said upstream ferrule (10a) and a plurality of stepped passages (21) formed by smaller-area upstream bores (22) and larger-area downstream bores (24) paired with each other in mutual register and interconnected through a first abrupt widening step (23), said upstream bores being separated by major solid radial parts and said downstream bores being separated by minor solid radial parts of smaller minimum width (2 than that (e ).of said major radial parts, and Y a downstream annular section having an outer end flange (16) fast with said downstream ferrule (10b) and an overhung tongue (19) defining therewith a circumferentially continuous duct (20) into which said downstream bores (24) open through a second abrupt widening step (30),

whereby said integral union member (13) has a passage area which increases suddenly twice, once at said first abrupt widening step (23) at the junction of said upstream and downstream bores (22, 24),

uniform passage area, the second passage area being in excess of the first and the third passage area being in excess of the second.

3. A flame tube as claimed in claim 1, wherein said upstream bores (22) have a cylindrical inner surface and said downstream bores (24) have an at least part cylindrical inner surface of larger diameter (d than that (d,)-of said upstream bores, said surfaces being substantially coaxial.

4. A flame tube as claimed in claim 3, wherein said downstream bores have a part cylindrical inner surface (24b) which is connected to the cylindrical inner surface (22b) of said upstream bores through apart circular abrupt widening step (23), whereby said downstream bores are partly trough-shaped and partly annular-shaped.

S. A flame tube as claimed in claim 4, wherein said trough-shaped part (28) and said annular-shaped part 29 of said downstream bores (24b) are respectively located toward the inside and the outside of the flame tube.

6. A flame tube as claimed in claim 3, wherein said downstream bores have a full cylindrical inner surface (24) whichis connected to the cylindrical inner surface (22) of said upstream bores through a full circular abrupt widening step (23). 

1. A multi-ferrule flame tube having an upstream ferrule (10a), a downstream ferrule (10b) stepped outwardly with respect to said upstream ferrule, and an integral union member (13) interposed between said ferrules and comprising: an upstream cannular-like section (14) having an inner end flange (15) fast with said upstream ferrule (10a) and a plurality of stepped passages (21) formed by smaller-area upstream bores (22) and larger-area downstream bores (24) paired with each other in mutual register and interconnected through a first abrupt widening step (23), said upstream bores being separated by major solid radial parts and said downstream bores being separated by minor solid radial parts of smaller minimum width (e2) than that (e1) of said major radial parts, and a downstream annular section (20) having an outer end flange (16) fast with said downstream ferrule (10b) and an overhung tongue (19) defining therewith a circumferentially continuous duct (20) into which said downstream bores (24) open through a second abrupt widening step (30), whereby said integral union member (13) has a passage area which increases suddenly twice, once at said first abrupt widening step (23) at the junction of said upstream and downstream bores (22, 24), and again at said second abrupt widening step (30) at the junction of said downstream bores (24) and said circumferentially continuous duct (20).
 2. A flame tube as claimed in claim 1, wherein said upstream bores (22), said downstream bores (24) and said circumferentially continuous duct (20) respectively have a first, a second and a third substantially uniform passage area, the second passage area being in excess of the first and the third passage area being in excess of the second.
 3. A flame tube as claimed in claim 1, wherein said upstream bores (22) have a cylindrical inner surface and said downstream bores (24) have an at least part cylindrical inner surface of larger diameter (d2) than that (d1) of said upstream bores, said surfaces being substantially coaxial.
 4. A flame tube as claimed in claim 3, wherein said downstream bores have a part cylindrical inner surface (24b) which is connected to the cylindrical inner surface (22b) of said upstream bores through a part circular abrupt widening step (23), whereby said downstream bores are partly trough-shaped and partly annular-shaped.
 5. A flame tube as claimed in claim 4, wherein said trough-shaped part (28) and said annular-shaped part 29 of said downstream bores (24b) are respectively located toward the inside and the outside of the flame tube.
 6. A flame tube as claimed in claim 3, wherein said downstream bores have a full cylindrical inner surface (24) which is connected to the cylindrical inner surface (22) of said upstream bores through a full circular abrupt widening step (23). 